1. Field of the Invention
This invention relates to a signal reproducing apparatus and more particularly to a signal reproducing apparatus which is provided with a circuit for correcting the time base of a reproduced signal.
2. Description of the Related Art
In the conventional signal reproducing apparatus of the above stated kind, such as a video tape recorder (hereinafter referred to as VTR) of the known low band converting type, a time base correction circuit (or a time base corrector, hereinafter referred to as TBC) has been arranged to give a time base corrected carrier chrominance signal by stepping up a horizontal synchronizing signal which is extracted from a reproduced video signal by means of a PLL circuit to a low-band converted carrier chrominance signal frequency; and by frequency converting a low-band converted carrier chrominance signal with a signal obtained by frequency converting a signal produced from a voltage controlled oscillator (hereinafter referred to as VCO) which is controlled on the basis of the stepped up horizontal synchronizing signal and a phase difference between the output of a reference oscillator and a reproduced color burst signal.
In addition to correcting the time base of the carrier chrominance signal, there has been contrived a method for correcting, at the same time, the time base of a luminance signal. In accordance with this method, the reproduced video signal is supplied to a variable delay line consisting of a CCD delay line; time base variations are extracted by using the above stated horizontal synchronizing signal; and the delay time obtainable by the variable delay line is controlled for correcting the time base of the luminance signal.
The above stated TBC of the conventional VTR has presented the following problem. In shifting from one to another the so-called normal reproduction mode and a special reproduction mode such as a high speed search mode or a slow reproduction mode, the synchronizing signal extracted from the reproduced video signal is apt to be disturbed by the dislocated servo lock of frequency and phase of the rotation of a drum and a capstan. The TBC malfunctions when the frequency and phase deviations come to exceed the correctable range of the TBC. The malfunction has disturbed a picture thus reproduced. To prevent such disturbance of the reproduced picture, varied methods have been developed including among others. A method of not allowing the TBC to operate in the special reproduction modes. Another method wherein a signal indicative of each special reproduction mode is produced; and after change-over to a special reproduction mode, the TBC is kept inoperative during a period of time set for the mode indicated by the signal.
The former method, however, prohibits the use of the TBC for special reproduction. Meanwhile, the latter makes the arrangement of the apparatus more complex accordingly as the number of special reproduction modes increases. Besides, it is difficult to set the periods of time during which the TBC must be kept inoperative.
Further, there are occurrences of some time base variations that are hardly pursuable by the TBC due to some reason other than the special reproduction. In such a case, the conventional time base correction circuit rather has brought about some adverse effect on reproduced signals.